Radio frequency identification (RFID) technology has experienced increased application in the manufacturing process and industry in recent years. From supply chain logistics to enhanced shop floor control, this technology presents opportunities for process improvement or re-engineering. The underlying principle of RFID technology is to obtain information from an RFID tag (“tag”) by using a RFID reader (“reader”) through radio frequency (RF) communication. The tag can be incorporated into or attached to a product, material, equipment, or person. In passive RFID systems, the tag does not include an internal power source and is activated by harvesting energy from a carrier signal received from the reader. Once activated, the tag responds to the reader through backscatter communication. This backscatter communication may include information that identifies the passive tag, and/or information about the item associated with the tag.
A network of distributed readers can be used to monitor the flow of tags and provide visibility in a manufacturing environment. For example, each RFID reader may be operatively associated with a central computer that determines the location of the tagged product or material based on the particular RFID reader that detected the passive tag's backscatter energy. Because readers have a maximum distance, or read range, at which they can communicate with a tag, it may be necessary to form a dense reader network by arranging readers relatively close to one another to obtain a desired coverage area within a particular process flow.
Readers can communicate with the tags using radio frequencies within approved bands such as a 431 MHZ to 478 MHZ band or an 862 MHZ to 956 MHz band. The selected band is divided into a plurality of channels of specified bandwidth (e.g., 200 kHz), and each reader can occupy a given channel or predetermined time period. When multiple readers are deployed in such a working environment, a carrier signal from one reader may reach another reader in the same channel at a certain distance and interfere with that reader's ability to read any tags within a certain range. This RFID interference problem is referred to as Reader Collision, and has been classified as frequency and tag interference. Frequency interference occurs when readers operating in the same frequency channel introduce high noise levels at each other, thereby interfering or jamming the on-going communication with tags. Tag interference occurs when multiple readers are attempting to read a tag at the same time regardless of the differences in frequency. Consequently, Reader Collision causes tags to be unreadable and disturbs the normal operation of the readers by lowering the overall read rates.